This application relates generally to fiber optics and more specifically to fiber optic routing devices.
For high bandwidth fiber optics communication systems, an important functional requirement is the ability to switch optical signals with low loss and low crosstalk. That is, an effective optical switch should switch a significant fraction of the light to the intended channel and substantially none of the light to unintended channels. Crosstalk is typically expressed in terms of attenuation (measured in decibels or dB), and xe2x88x9250 dB is generally considered a target performance level. A crossbar switch is a matrix of switching elements for switching optical signals from a set of signal-carrying input optical fibers to a set of output optical fibers. In addition to the functional performance characteristics mentioned above, it is desirable that the switch be fast, reliable, compact, and inexpensive.
Prior art optical switches include (1) opto-mechanical devices (using moving micro-optics), (b) thermo-optical polymer waveguides, (c) micro-electromechanical (MEMS), and (d) index matching fluid with movable bubbles in trenches in a planar waveguide. While all of these technologies have been demonstrated for optical switches, considerable efforts are still ongoing to develop an all optical crossbar switch characterized by low loss and crosstalk, high speed and reliability, small overall size, and low cost.
An additional important functionality is to provide add/drop wavelength multiplexing. An add/drop multiplexer will extract one or more wavelength channels from a multi-wavelength optical communications link and inject one or more wavelength channels carrying different information. As is well known, typical single-mode, fiber optics communications are at wavelengths in the 1300-nm and 1550-nm ranges. The International Telecommunications Union (ITU) has defined a standard wavelength grid having a frequency band centered at 193,100 GHz, and other bands spaced at 100 GHz intervals around 193,100 GHz. This corresponds to a wavelength spacing of approximately 0.8 nm around a center wavelength of approximately 1550 nm, it being understood that the grid is uniform in frequency and only approximately uniform in wavelength.
The present invention provides an optical routing element (ORE) characterized by low insertion loss, low crosstalk, ease of manufacture, and low cost.
The ORE includes first, second, and third waveguide segments. The first and second waveguide segments extend along a common axis, and are separated by a routing region. The third waveguide segment extends from the routing region at a non-zero angle with respect to the common axis. In some embodiments, the routing region is occupied by a selectively reflecting element. The selectively reflective element selectively reflects light based on a state of the element or a property of the light.
In some switch embodiments, the selectively reflecting element is a thermal expansion element (TEE) that includes a body of material (such as a polymer material) having contracted and expanded states at respective first and second temperatures. The contracted state defines an air gap disposed in the path of light traveling along the first waveguide segment so as to cause the light to be deflected into the third waveguide segment through total internal reflection. The expanded state removes the air gap so as to allow the light traveling along the first waveguide segment to pass into the second waveguide segment.
In a preferred construction, the first, second, and third waveguide segments are formed in a monolithic planar waveguide device, and a trench is formed across the region where the waveguide segments intersect. A selectively reflecting element, such as a TEE, is disposed in the trench. Communication with the ORE is typically effected through optical fibers that are in optical contact with the waveguide segments at respective positions at the edges of the planar waveguide device.
In some embodiments, the optical fibers have flared cores. That is, the cores gradually expand so that they have a larger diameter where they contact the planar waveguide device. This allows the transverse dimensions of the waveguide segments to be larger, which eases the manufacture and allows more flexibility in the design of the selectively reflecting element. The transition to the larger diameter is sufficiently gradual that single-mode propagation in the fiber is maintained.
In some embodiments, the selectively reflecting element is a wavelength selective filter. OREs according to different embodiments of the invention are readily incorporated into a variety of configurations, to provide the basis for such devices as crossbar switches, wavelength division multiplexers, and add/drop multiplexers.
A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings.